The Status of \u3ci\u3eDiporeia\u3c/i\u3e spp. in Lake Ontario, 1994- 1997

Surveys of benthic macroinvertebrates conducted in Lake Ontario between 1994 and 1997 revealed a recent decline in Diporeia spp. (Amphipoda) abundance. The lowest population densities and summer biomass are in the eastern basin of the lake at all depths. Densities and biomass declined in the shallowest (10-50 m) depth zone between 1994 and 1997. Mean Diporeia spp. densities declined from 1412 m-2 to 1 m-2, and the total mean biomass declined from 0.66-g DW m-2 to 0.001 g-DW m-2. The latter represents an overall loss of about 5100 mt of biomass in the shallowest depth zone. In contrast, biomass at the deepest zone (\u3e90 m) did not change from 1994 to 1997 and has actually increased over twofold since 1972. This shift of total biomass from shallow to deeper sediments will have a profound effect on organisms that depend upon Diporeia spp. for food. Because of the importance of benthic macroinvertebrates, and particularly Diporeia spp. in fish diets, changes in the status of Diporeia spp. could have dramatic effects on fish production in Lake Ontario